In various types of signal and communication systems for use in railroad and mass and/or rapid transit operations, it is is customary practice to employ cab signals to control the speed of a vehicle or train as it moves along its route of travel. Normally, the cab signals which are received on board the vehicle or train are in the form of coded carrier waveforms. That is, the carrier signal is selectively coded or modulated by one of a plurality of code or pulse rates. Each code or pulse rate signifies or represents a given maximum speed or velocity at which a vehicle or train is permitted to travel along any given block or section of trackway. In actual operation, the coded carrier signals are normally conveyed to the track rails by a transmitter connected thereto and are picked up by inductive receiver coils which are mounted forward of the front axle of the lead vehicle or locomotive. The picked up signals are amplified, demodulated, shaped, and filtered, and then the recovered signals are applied to the speed command decoding unit. One necessary and important function to be carried out in a cab signaling operation is the ability for the car-borne equipment to detect and sense overspeed conditions. That is, when the actual speed of the moving vehicle or train exceeds the authorized speed permitted in a particular track section or block area, an overspeed signal is immediately produced on board to alert the operator or trainman of the violation. In practice, this speed check is accomplished by the overspeed control equipment or speed governor portion of the car-carried cab signaling equipment. In practice, an axle generator or tachometer in the form of a frequency generator is employed to produce a.c. signals which are proportional to the actual speed of the moving vehicle. In the past, a multi-section low-pass filter was used for each speed command, and the appropriate filter section was selected by the relay contacts of the speed command decoding unit. While one previous arrangement worked quite satisfactory, it was rather large and relatively expensive since a complete printed circuit board was required for every two-speed commands. In another arrangement, a single low-pass filter was employed for accommodating all of the vehicle speeds while the speed command signals were used to vary the turns ratio of a multi-tapped transformer. Thus, the necessary gain between the filter circuit and a level detector was varied by the closing of various decoding relay contacts connected to selected taps of the transformer which was driven by an emitter-follower amplifier. That is, by applying the emitter-follower power supply through the transformer taps, various levels of gain can be selected. Further, the current requirements are designed to be very low so that either a solid-state source or a relay contact could be reset to supply power. While this latter scheme could accommodate six to eight speeds per printed circuit board, there were several shortcomings or drawbacks in such an arrangement. First, the appearance of noise or extraneous signals on the speed command inputs could result in an increase in the authorized speed command level which could cause an erroneous and unsafe overspeed point. Second, certain subtle variations in the characteristics of the multi-tapped transformer could give rise to inaccurate results, and, third, the range of speeds which could be practically used with a filter-transformer combination was limited due to the finite amount of gain that is attainable with such an emitter-follower configuration.